-
[show abstract]
[hide abstract]
ABSTRACT: The use of coherent transition radiation autocorrelation methods to determine bunch length and profile information is examined with the compressed electron beam at the BNL ATF. A bi-gaussian fit is applied to coherent transition radiation auto-correlation data to extract the longitudinal current distribution. The effects of large transverse beam sizes are studied in theory and compared to experimental results. A suitable form of the correction factor is derived for beams with large transverse-longitudinal aspect ratios. Comment: 5 pages, 1 figures, submitted to The Second Workshop on High Average Power & High Brightness Beams (January 2009)
02/2010;
-
G Andonian,
A Cook, M Dunning,
E Hemsing,
G Marcus,
A Murokh,
S Reiche,
D Schiller,
J B Rosenzweig,
M Babzien,
K Kusche,
V Yakimenko
[show abstract]
[hide abstract]
ABSTRACT: Coherent radiation emitted from a compressed electron bunch as it traverses the sharp edge regions of a magnetic chicane has been investigated at the Brookhaven National Laboratory Accelerator Test Facility. Electron beam measurements using coherent transition radiation interferometry indicate a 100 fs rms bunch accompanied by distinct distortions in energy spectrum due to strong self-fields. These self-fields are manifested in emitted high power THz radiation, which displays signatures of the phenomenon known as coherent edge radiation. Radiation characterization studies undertaken include spectral analysis, far-field intensity distribution, polarization, and dependence on the electron bunch length. The observed aspects of the beam and radiation allow detailed comparisons with start-to-end simulations. Novel types of coherent electromagnetic radiation sources based on electron beams, extending in spectrum from THz to x rays, are presently under intensive develop-ment in the scientific community. For example, the x-ray free-electron laser (FEL) is a light source that will allow investigation of physical systems on the time and length scales of atomic motion (100 fs, 1 Å) [1], paving the way for revolutionary advances in biological and condensed matter sciences [2]. Such sources are based on emission from high brightness (high phase space density), relativis-tic electron beams undergoing magnetic bending forces. Specifically, x-ray FELs require short electron pulses si-multaneously having high charge and low energy spread, with small transverse normalized emittance, n . The requirements for achieving high-gain lasing in an x-ray FEL illustrate this basis, as one typically must enhance the beam current, I b , from 100 A at the source to several kA, while maintaining n on the order of 1 mm mrad. Obtaining such beams entails pulse compression, com-monly implemented by deploying a magnetic chicane ar-ray downstream of a radio-frequency linear accelerator (rf linac). The linac is operated off the phase of maximum acceleration, imparting a time-energy correlation, or en-ergy chirp, onto the beam. This chirp is then removed by the energy dependence of transport time through the chi-cane, thus yielding a beam shorter in time duration. The compression process provokes strong self-interactions in the beam, which manifest themselves in several ways. At lower energies (50 MeV), collective interactions are dominated by velocity field-derived ef-fects, which strongly distort the transverse phase space [3]. At higher energies, acceleration fields are stronger; these give rise to both coherent synchrotron radiation (CSR) and an associated strong energy modulation of the beam [4]. This modulation may bring about a microbunch-ing instability [5], which has strong similarities to the FEL instability [6]. Such collective effects degrade the beam's longitudinal and transverse phase space during compres-sion [7], and may severely impact the utility of a beam as an x-ray FEL lasing medium. Previous studies of picosecond pulses in bends have observed CSR [8] and associated beam phase space dis-tortions [3,9]. An interesting attribute of coherent radiation from bending electron beams is short wavelength (< 1 mm) [10] coherent edge radiation (CER). Edge radiation [11], which is created where the electrons enter and exit magnetic dipole field regions, has notable differences with respect to synchrotron radiation. In many respects it is similar to transition radiation, having a polarization com-ponent out of the bend plane, a hollow transverse spatial distribution, and a low-frequency spectral intensity nearly independent of frequency. Further, the frequency scaling of the coherent energy emitted (with =2 longer than the rms bunch length, z) via CER in an edge region is larger than that of CSR in the same relevant solid angle. There are many proposed practical applications which exploit these features of coherent edge radiation. For ex-ample, CER is attractive as a basis for bunch length diag-nosis. In particular, in future light sources, a nondestructive bunch profile monitor may be developed by exploiting the CER observed from the chicane magnet compressors em-ployed to achieve the necessary high peak current. Interferometric analysis of the produced CER would yield direct information about the beam temporal profile. CER is also of interest as a unique, high power source of coherent THz radiation, which has a myriad of scientific, industrial, and biomedical applications, such as organic molecule imaging [8]. Since CER production is of interest for, and is already finding [12], widespread applications, it is worth a more concerted effort to study the principles of this
Physical Review Special Topics - Accelerators and Beams 01/2009; 12:030701. · 1.52 Impact Factor
-
G. Andonian,
R. Agustsson,
A. Cook, M. Dunning,
E. Hemsing,
A. Murokh,
S. Reiche,
J. Rosenzweig,
M. Babzien,
K. Kusche,
R. Malone,
V. Yakimenko
[show abstract]
[hide abstract]
ABSTRACT: The radiation emitted from a chicane compressor has been studied at the Brookhaven national laboratory (BNL) accelerator test facility (ATF). Coherent edge radiation (CER) is emitted from a compressed electron beam as it traverses sharp edge regions of a magnet. The compression is accompanied by strong self-fields, which are manifested as distortions in the momentum space called beam bifurcation. Recent measurements indicate that the bunch length is approximately 150 fs rms. The emitted THz chicane radiation displays strong signatures of CER. This paper reports on the experimental characterization and subsequent analysis of the chicane radiation measurements at the BNL ATF with a discussion of diagnostics development and implementation. The characterization includes spectral analysis, far-field intensity distribution, and polarization effects. Experimental data is benchmarked to a custom developed start-to-end simulation suite.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
-
[show abstract]
[hide abstract]
ABSTRACT: An experimental study of a seeded Free Electron Laser (FEL) using the VISA undulator and a Nd:YAG seed laser will be performed at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory. The study is motivated by the demand for a short Rayleigh length FEL amplifier at 1 micron to allow for high power transmission with minimal damage of transport optics. Planned measurements include transverse and longitudinal coherence, angular distribution, and wavelength spectrum of the FEL radiation. The effects of detuning the electron beam energy will be studied, with an emphasis on control of the radiation emission angles and increase of the amplifier efficiency. Results of start-to-end simulations are also presented.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
-
J. B. Rosenzweig, M. Dunning,
E. Hemsing,
G. Andonian,
A. M. Cook,
A. Murokh,
S. Reiche,
D. Schiller,
M. Babzien,
K. Kusche,
V. Yakimenko,
L. Palumbo,
C. Vicario
[show abstract]
[hide abstract]
ABSTRACT: We review recent experimental results from the BNL ATF using the compressor built by UCLA. The measurements discussed include: first observation of short wavelength coherent edge radiation angular/wavelength spectrum and spectrum, sub‐100 fsec pulse‐length coherent transition autocorrelation measurements, and longitudinal and transverse phase space distortions. Extension of these measurements, as well as those which can be made possible by a new X‐band traveling wave deflector being developed in an industrial collaboration, are examined. © 2006 American Institute of Physics
AIP Conference Proceedings. 11/2006; 877(1):642-648.
-
[show abstract]
[hide abstract]
ABSTRACT: The VISA (Visible to Infrared SASE Amplifier) program has been in operation at the BNL ATF since the year 2000. The program has produced numerous results including, demonstrated saturation at 840 nm with a gain length of 18 cm, chirped beam amplification with the observation of anomalously large bandwidth of the emitted radiation, and successful benchmarking of a start-to-end simulation suite to measured results. This paper will review the prior results of the VISA program and discuss planned novel measurements, including detuning studies of a seeded amplifier, and measurements of the orbital angular momentum of the emitted radiation. The installation of a dedicated chicane bunch compressor followed by an x-band linac to mitigate energy spread will allow for high-current operations (reduced saturation length, and deep-saturation studies). Other measurements, such as coherent transition undulator radiation, are also proposed.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
